The invention is particularly suited for toothed rack steering systems that are very often utilized in motor vehicles. A rotating steering movement applied through the steering wheel is converted into a rectilinear movement for pivoting the vehicle wheels to be steered. For this purpose, the end of a steering column of the vehicle is connected to a pinion that engages the toothed rack and displaces it laterally upon rotation of the steering system. On either end of the toothed racks a steering tie rod is connected through a universal joint. The pinion, which is connected to the steering column, is disposed inside a valve tower which is in turn connected to a toothed rack housing surrounding the toothed rack. The toothed rack housing and the valve tower comprise openings that coincide (i.e., correspond to one another) in the mounted condition and form an engagement region for the pinion.
On current power steering systems, rotary servo valves are known for controlling hydraulic pressure and, as a result thereof, steering assistance on an assistance cylinder as a function of the applied steering torque of the driver. In most cases, rotary servo valves are being utilized in which an input shaft, which is connected to the steering wheel through the steering column, rotates relative to a control sleeve which is connected to the output shaft and, in case of toothed rack steering systems, to the pinion. Through a torsion system between input shaft and control sleeve a rotating angle of the valve and, as a result thereof, a torque-dependent valve characteristic is realized. Accordingly, rotation of the input shaft relative to the control sleeve provides the auxiliary force needed for steering.
Accordingly, the input shaft is connected to a first valve element that is configured to be a rotary slide valve located radially inside. The control sleeve is located radially outside of and surrounds this first valve element. Both valve elements comprise control grooves serving to control the pressure means coming from or flowing to work chambers of the servo motor. The control grooves may however also be disposed directly on the input shaft. The manufacturing of these component parts is subject to the highest quality requirements with regards to material selection and production accuracy. Insofar, such type component parts are devised to be short, with the smallest possible dimensions, and are connected in the vehicle to component parts of the steering column that have to meet less stringent quality requirements.
Since the end of the valve tower and the steering wheel are spaced a large distance apart, it is necessary to use quite long steering columns that are often angled through hinges. In order to avoid bearing damages in the region of the valve tower, steering columns are often carried rotatably on several points. The bearings are thereby usually disposed in the region of the bodywork with the steering column extending therethrough. Insofar, the arrangement and positioning of the bearings are essential for steering quality and for less wear of the device over its lifetime. The bearings must be positioned accurately to achieve the desired effects.